The present invention relates to a copper-based alloy for use in electrical and electronic devices, particularly, as a material for lead frames of semiconductor devices.
Materials for lead frames of semiconductor devices should have high electrical conductivity, high mechanical strength, high durability against repeated bending, affinities for plating materials and solders, and heat durability, as well as various other properties including low thermal expansion coefficient.
Generally, FE--Ni 42 alloys, which are high in mechanical strength and low in thermal expansion coefficient, have been used for this purpose. However, the use of copper alloys for the same purposes is increasing due to the need to accommodate semiconductor devices of increased power while providing a reduced cost.
Ideal properties of a material of semiconductor lead frames includes a tensile strength of 50 kg/mm.sup.2 or more, elongation of 10% or more, and electrical conductivity of 50% IACS or more. However, there is no known material which can simultaneously satisfy all of these requirements. Usually phosphor bronze is selected when the mechanical strength and bending durability are predominant requirements and copper-based alloy coated materials when conductivity and cost are predominant. However, conventional phosphor bronze exhibits a low conductivity and is high in cost because the cost of Sn is high. Copper alloys, on the other hand, are generally low in mechanical strength and durability for repeated bendings.